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Vampire vine helps to destroy alien European weeds in Australia

Let the plant wars begin. A parasitic vine that sucks the life out of feral weeds is being billed as a promising new agent for biocontrol.

Cassytha pubescens, or devil’s twine, is the first native plant to be investigated as a weapon against invasive weeds introduced to Australia by European settlers in the early 1800s.

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Robert Cirocco of the University of Adelaide says the vine is able to kill all the “major baddies” – gorse, Scotch broom and blackberry – by attaching small suckers to the plants’ stems and extracting their water and nutrients.

“This is important because these weeds cost us millions of dollars annually to eradicate, not to mention their incalculable costs to our native biodiversity,” he says.

The most notorious of these alien weeds, European gorse (Ulex europaeus), costs more than A$7 million (US$5.5 million) each year to clear from natural habitats and farmland with a mixture of herbicides, mechanical removal and burning.

Cirocco and his colleagues showed that devil’s twine can destroy gorse by reducing its water and nutrient intake, which in turn harms photosynthesis. “Less photosynthesis translates to less carbohydrate, and less carbohydrate translates to less growth,” says Cirocco

Dead gorse

The gorse plants that the researchers studied were in the Mount Lofty Ranges in South Australia, where many had been naturally infected with C. pubescens in the area. “You could see a Cassytha infection front that was leaving dead gorse in its wake,” says Cirocco.

The work was presented at the Natural Resource Management Science Conference in Adelaide last week.

According to Cirocco, the biggest advantage of C. pubescens as a potential biocontrol agent is that it already occurs naturally across large tracts of eastern Australia.

As a result, there is little danger that the vine will itself become a menace, as with the cane toads introduced to Australia in 1935 to control beetles that devastated sugar-cane crops.

C. pubescens also fulfils the brief of being far more toxic to non-native than native plants.

“Cassytha is not the smartest thing – it will pretty much go for anything it can get its suckers on, including barbed wire,” says Cirocco. “But research shows that Cassytha has a much greater effect on invasive weeds, perhaps because native plants have co-evolved with it, so they have likely developed mechanisms of resistance or tolerance.”

Native biocontrol

Cirocco says the next step will be to conduct field trials to confirm the effectiveness of C. pubescens against gorse in a variety of natural habitats.

“Cassytha continues to show promise as an effective native biocontrol against major invasive weeds, so it’s definitely worth exploring,” he says.

The strategy makes sense from an ecological point of view, but the success of biocontrols is very difficult to predict, says Roger Cousens of the University of Melbourne.

“You never can tell with biocontrol agents. You carefully select them and do all the work but quite often they just don’t do the job,” he says. “But when they do work, it’s fantastic.”

Leslie Weston of the Charles Sturt University in Wagga Wagga, New South Wales, agrees that the strategy has potential. “The issue is how you manage the Cassytha itself once it’s established because it’s obviously not something you want to be extended past its natural range,” she says. “Although Cassytha might not have an as adverse effect on the natives, it can still have an effect.”

“Usually when you pick a biocontrol organism, you pick one that is incredibly specific to the host you’re trying to decimate. This is a non-specific option so it would have to be very carefully managed,” says Weston.